1. Field of the Invention
The invention relates to the field of pneumatic supports, such as those implemented in various machines, more particularly vehicle engines.
2. Description of the Related Art
In the first place, it should be mentioned that such pneumatic supports may be referred to by different terms depending on the manufacturers, for example, but that this list is not exhaustive: pneumatic damping devices, vibration-damping supports, air springs, vibration absorbers, shock absorbers, etc. The term “pneumatic support” used here must be considered as referring to the same thing as what is designated by the other mentioned expressions, i.e. a device interposed between and made integral with a first part such as a carrier structure and a second part such as a driving system, intended to limit the vibrations liable to be transmitted between the parts, one of which at least is moving or can be moved, and specifically can vibrate. Thus, the term “pneumatic support”, as such, is not limitative.
It is common knowledge that such pneumatic supports are commonly used. They are also the subject of a number of achievements, such as those disclosed in documents EP 2141381, KR 2011 106072, KR 20110 53648, U.S. 2011/10042873, U.S. Pat. No. 6,902,156, U.S. Pat. No. 4,407,494, U.S. Pat. No. 4,700,931, U.S. 2010/0001447, JP 57160716, DE 19952638, DE 102004008401, WO 2008/015247, U.S. 2009/0266333, U.S. 2009/0309279, U.S. 2010/0140857, U.S. 2001/01012 and U.S. 2010/0025901.
More specifically, the document U.S. 2010/0025902 or other similar documents describe such a pneumatically damping mount comprising a first carrier means adapted to secure the rigid connection of the pneumatic support to one of the two parts, a second carrier means adapted to ensure the rigid connection of the pneumatic mount to the other part, a first spring means and a second spring means.
The first carrier means comprises a rigid wall having with a side portion provided with a large opening and, an opposite transverse portion provided with one or more small opening(s), and defines a cavity having on one side the large opening and on the other side the small opening(s).
The first spring means, which comprises an elastomeric material, is interposed between and made rigidly integral, toward its side periphery, with the side portion of the wall of the first carrier means towards the large opening, and toward its outer transverse periphery with the second support means. It has a middle transverse face oriented toward and separated from the transverse portion of the wall of the first carrier means.
The second spring means, which also comprises an elastomeric material, is made rigidly integral, toward its side periphery, with the side portion of the wall of the first carrying means, toward its transverse portion. It has a middle transverse face and an opposite face positioned opposite the transverse portion of the wall of the first carrier means. According to the document U.S. 2010/0025902, such opposite face has undulations with recesses and protrusions, with the protrusions being in contact with the transverse portion of the wall of the first carrier means.
The two middle transverse faces of the first spring means and the second spring means are positioned opposite each other and provide a first deformable working chamber adapted to receive a gas, particularly atmospheric air, whereas what the document U.S. 2010/0025902 calls a second “working chamber” is provided between the opposite contacting faces, i.e. the opposite face of the second spring means, which is not flat but instead significantly undulated with recesses and protrusions, and the inner face of the transverse portion of the wall of the first carrier means.
A hole is provided in the second spring means, so as to provide communication between the first working chamber on one side, and the small opening(s) and thus the atmospheric air on the other side.
The document U.S. 2010/0025902 and in particular its force/displacement graph, demonstrates that the first working chamber is the important element. It is active when its volume is positive and remains active when its volume decreases and possibly reaches zero when the two middle transverse faces of the first and second spring-forming members are in contact with and pressed against each other. As mentioned, if additional pressure is then applied, the second spring means is compressed. Further deformation is then obtained. As a matter of fact, the second working chamber makes it possible to increase the elasticity of the second spring means when pressure is applied thereto.
It appeared to the applicant that a second spring means which, first, has a so-called “opposite face” (i.e. a face positioned opposite the transverse portion of the wall of the first carrier means) which does not extend along a general transverse direction since it has significant undulations with recesses and protrusions, with the protrusions being in contact with the transverse portion of the wall of the first carrier means, secondly has a thickness varying over a wide range (i.e. a thickness varying from one to three according to the figures in document U.S. 2010/0025902), affects the performance of the pneumatic support, particularly as regards damping because, when the volume of the first chamber is null because the two middle transverse faces of the first and second spring-forming members are in contact with and pressed against each other, the movement of the second spring means causes a very high variation of the force.
The document FR 1492 121 aims at a shock and vibration absorbing device between two elements such as frames or parts, comprising a housing integral with one of the elements, on the bottom of which an elastic membrane, so-called a carrier membrane, is provided and inside which a second antagonistic membrane integral with the second element is provided, in particular having the characteristic consisting in that, to improve the damping characteristics, the carrier membrane is provided with at least one hole and the side wall of the housing is provided with at least one hole in its part located between the two membranes, with such holes having a small diameter.
The document U.S. Pat. No. 7,341,244 relates to a hydraulic anti-vibration support comprising an elastomer spring body which connects a first rigid strength member and a second rigid strength member. The first rigid strength member includes a piston which comprises a rod terminated by an end member, and the second rigid strength member has an opening which is gone through by said piston. A liquid-filled module is mounted inside a housing which is secured to the second rigid strength member, and includes a working chamber defined in part by a substantially dome-shaped elastomer wall which has a central area in contact with the end member of the piston without any mechanical securing.
There is therefore a need for pneumatic supports of the type previously mentioned which do not have such drawbacks. This is the problem underlying the invention. As a matter of fact, the issue consists in limiting the volume without being in saturation, so as to have a limited volume in the area of deformation within a given range and a second chamber which takes over to still have edge.